Kerala Plus Two Chemistry key terms

The number of moles of solute dissolved in one kilogram of solvent. Because it uses mass rather than volume, molality does not change with temperature and is preferred for colligative-property calculations.

A property of a dilute solution that depends only on the number of solute particles present, not on their identity. Examples include relative lowering of vapour pressure, boiling-point elevation, freezing-point depression and osmotic pressure.

The ratio of the observed colligative effect to the value expected for a non-dissociating solute, equal to the actual number of particles produced per formula unit. It exceeds one for dissociation and falls below one for association.

For a solution, the partial vapour pressure of each volatile component is proportional to its mole fraction. For a non-volatile solute, the relative lowering of vapour pressure equals the mole fraction of solute.

The potential of a half-cell measured relative to the standard hydrogen electrode under standard conditions of concentration or pressure, usually 298 K. It measures the tendency of a species to be reduced.

An equation relating cell potential to standard cell potential and reaction quotient, E = E° − (RT/nF) ln Q. At 298 K it becomes E = E° − (0.0591/n) log Q for a reaction involving n electrons.

The conductance of a solution containing one mole of electrolyte placed between electrodes one centimetre apart, expressed in S cm² mol⁻¹. It increases on dilution because ion–ion interactions weaken.

The limiting molar conductivity of an electrolyte equals the sum of the limiting molar conductivities of its individual ions, each multiplied by its stoichiometric coefficient. It allows calculation of limiting conductivity for weak electrolytes and of the degree of dissociation.

The electrochemical deterioration of a metal, as in rusting of iron where iron is oxidised at anodic regions and dissolved oxygen is reduced at cathodic regions. Moisture and electrolytes accelerate the process.

The proportionality constant in a rate law that equals the reaction rate when all reactant concentrations are unity. Its value depends on temperature and catalyst presence, not on concentration.

The sum of the powers to which reactant concentrations are raised in the experimentally determined rate law. It may be zero, fractional or negative and need not match the stoichiometric coefficients.

The time required for the concentration of a reactant to fall to half its initial value. For a first-order reaction it is independent of initial concentration and equals 0.693 divided by the rate constant.

An equation expressing the temperature dependence of the rate constant, k = A e^(−Ea/RT), where A is the frequency factor and Ea the activation energy. A plot of ln k against 1/T is linear.

An element whose atoms or common ions have a partly filled d subshell, or which can form such ions. This produces variable oxidation states, coloured compounds, catalytic activity and magnetic behaviour.

The steady decrease in atomic and ionic radii across the lanthanoid series as nuclear charge rises while 4f electrons shield poorly. It makes the second and third transition series resemble each other in size.

A compound formed when small atoms such as hydrogen, carbon or nitrogen occupy holes in a metal lattice. Such compounds are usually hard, retain metallic conductivity and often have non-stoichiometric compositions.

An ion or molecule that donates one or more electron pairs to a central metal ion to form a coordinate bond in a complex. Examples are ammonia, chloride, cyanide and ethylenediamine.

The number of donor atoms directly bonded to the central metal ion in a coordination entity. It is commonly four, giving tetrahedral or square planar geometry, or six, giving octahedral geometry.

The separation of the five d orbitals of a metal ion into sets of different energy when ligands approach, as in an octahedral field where t2g lies below eg. The gap size determines colour and magnetic behaviour.

The extra stability of complexes formed by polydentate ligands that close rings around the metal ion, compared with analogous monodentate complexes. It arises largely because fewer particles are produced on dissociation.

A nucleophilic substitution in which the leaving group departs first to form a carbocation, which the nucleophile then attacks. It is first order, favoured by tertiary halides and polar protic solvents, and leads to racemisation.

A one-step nucleophilic substitution in which the nucleophile attacks the carbon from the side opposite the leaving group through a five-coordinate transition state. It is second order, favoured by primary halides, and inverts configuration.

The property of a molecule that is not superimposable on its mirror image. Chiral molecules rotate the plane of polarised light and exist as enantiomeric pairs with identical physical properties except optical rotation.

The preparation of an ether by treating an alkyl halide with a sodium alkoxide in an SN2 reaction. Primary halides give the best yields, while tertiary halides favour elimination and give alkenes.

A test distinguishing primary, secondary and tertiary alcohols by the time taken to form a cloudy alkyl chloride layer when the alcohol is shaken with concentrated hydrochloric acid and anhydrous zinc chloride.

The formylation of phenol with chloroform and aqueous sodium hydroxide, giving mainly salicylaldehyde, that is 2-hydroxybenzaldehyde. The reaction proceeds through a dichlorocarbene intermediate and shows electrophilic substitution at the ortho position.

The base-catalysed addition of an enolate from one aldehyde or ketone to the carbonyl carbon of another, forming a β-hydroxy carbonyl compound that may lose water to give an α,β-unsaturated product.

The base-induced disproportionation of aldehydes lacking α-hydrogens, such as benzaldehyde or methanal, producing equimolar amounts of the corresponding carboxylate salt and alcohol in a single reaction.

An ammoniacal silver nitrate solution that oxidises aldehydes to carboxylate ions while depositing metallic silver as a mirror on the vessel. Ketones and most other functional groups give no reaction.

A method of classifying primary, secondary and tertiary amines by reaction with benzenesulfonyl chloride: primary amines give a soluble sulfonamide, secondary amines an insoluble solid, and tertiary amines no reaction.

A compound containing the –N₂⁺ group attached to an aromatic ring, usually made by diazotising a primary aromatic amine with nitrous acid at 273–278 K. It is a versatile intermediate for substitution and coupling reactions.

The reaction of a diazonium salt with phenol or an aromatic amine in a mildly alkaline or acidic medium to give an intensely coloured azo compound, widely used in dye synthesis.

Cyclic stereoisomers of a monosaccharide that differ only in the configuration at the anomeric carbon, the hemiacetal carbon created on ring closure. The pair is designated alpha and beta.

An ion carrying both positive and negative charges, as in an amino acid at its isoelectric point where the carboxyl group is deprotonated and the amino group protonated. Such ions have no net charge overall.

Loss of the native three-dimensional structure and biological activity of a protein caused by heat, pH change, alcohol or heavy-metal ions. The primary structure usually remains intact.

A highly pure, stable substance of known composition used to prepare a standard solution or to standardise another solution. Examples include oxalic acid, potassium hydrogen phthalate and sodium carbonate.

In chromatography, the distance travelled by a solute divided by the distance travelled by the solvent front from the origin, measured under identical conditions. It helps identify the components of a mixture.

A preliminary test in organic analysis in which the sodium fusion extract of a compound is tested for nitrogen, sulphur and halogens using iron(II) sulphate, dilute acid and silver nitrate.